Respiratory syncytial virus infection (RSV) is a major cause of severe respiratory disease in infants and young children, often requiring intensive care hospitalization. Despite considerable effort there is no safe and effective vaccine for RSV. A formalin-inactivated RSV vaccine resulted in potentiation of disease in naturally infected children. Bovine RSV (BRSV) is a closely related virus, which causes a similar disease in young calves; clinical, immunological, and pathological features are nearly identical. To achieve the longterm objective of development of a safe and effective vaccine for RSV, this proposal will use a BRSV infection model. Calves develop moderate to severe disease alter experimental Infection with a field isolate. The model is unique in that a chronic lung lymph fistula has been surgically created for the monitoring of lymphocytes and lymph fluid. Specific Aims are: 1) to determine the relationship between the type and magnitude of the immune response to BRSV proteins and severity of experimental infection in calves vaccinated with formalin-inactivated (FI) vaccine, 2) to compare and contrast the effects of BRSV infection in FI-vaccinated and naive calves on pulmonary function, cytokine production, T cell sub-populations, eicosanoid production, immunoglobulin production, virus shedding, lung pathology, and clinical signs, 3) to evaluate the potential for eliciting a protective mucosal immune response by aerosol immunization of calves with recombinant fusion protein in a liposome carrier, and 4) to compare RSV and BRSV fusion protein with respect to their immunogenicity and protection provided when maternal immunity is present. These specific aims will be addressed in three experiments. In the first experiment the FI- vaccine induced immunopotentiation will be reproduced using two different intervals between vaccination and virus exposure to determine the effect of early versus later viral challenge. Mock-vaccinated and mock-infected control groups will be included. Lung lavage and pulmonary function testing will be performed. Data gathered will include: BRSV-specific IgG, IgA, IgE, virus neutralization, leukotriene C4, B4, and prostaglandins E2, F2alpha, D2, and thromboxane B2, lung pathology, and lung immunohistochemistry to evaluate antibody and complement localization. MHC class II expression and T cell subset identification will be done in blood and lung tissue. Lung tissue morphometry will quantitate and identify airway-associated cellular accumulations. Cellular responses will be evaluated by lymphocyte stimulation and cytotoxicity. Concentration of histamine and virus recovery will be monitored in nasopharyngeal secretions daily during infection. In experiment two lung lymph fistulas will be created to monitor the above parameters in lymph, as well as lung lymph cell gene expression for interleukin 4 and gamma interferon. Experiment three will combine lymphatic cannulation with immunization of separate groups of calves by aerosol with either recombinant BRSV F protein or RSV F protein in liposome carrier, or a liposome control. Results of BRSV challenge will aid in determining the potential for a crossreactive F protein to elicit protection when maternal antibody is present. In summary, three experiments will be performed using a calf-BRSV infection model to evaluate vaccine protection and immunopotentiation of disease.